Production of Syngas from Biomass Using a Downdraft Gasifier

Hassan Golpour.et.al. Int. Journal of Engineering Research and Application www.ijera.com
ISSN : 2248-9622, Vol. 7, Issue 6, (Part -2) June 2017, pp.61-71
www.ijera.com DOI: 10.9790/9622-0706026171 61 | P a g e
Production of Syngas from Biomass Using a Downdraft Gasifier
Hassan Golpour, PhD1
, Teja Boravelli2
, Joseph D. Smith, PhD3
,
Hamid R. Safarpour4
1
Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA
2
Departments of Chemical and Biochemical Engineering, Missouri University of Science and Technology,
Rolla, MO, USA
3
Departments of Chemical and Biochemical Engineering, Missouri University of Science and Technology,
Rolla, MO, USA
4
Department of System Engineering, Missouri University of Science and Technology, Rolla, MO, USA
ABSTRACT
The role of biomass in energy and fuel production as an alternative to fossil fuel is vitally important considering
carbon dioxide production vs. secure energy. Sustainable, renewable and reliable resources of domestically
produced biomass together with wind and solar energy are sensible options to support a small-scale power
generation to meet local electricity demand plus provide heat for rural development. The present work focuses
on:
1. Design, build and operate a vertical downdraft biomass gasifier with tar removal
2. Establishing the optimum operating methodology and parameters to maximize syngas production in biomass
gasification through process testing.
The one ton per day biomass gasification process unit designed in this work included a downdraft biomass
thermochemical conversion gasifier, gas transportation line with tar removal and an enclosed combustion
chamber. The reactor used internal heat transfer surfaces to enhance intra-bed heat and mass transfer inside the
reactor. Three different woody biomass feedstock including pellets, picks and flakes were examined in this
work. Specific results described in this paper include identifying and characterizing the key operating factors
(i.e., temperature profile, feed stock carbon/hydrogen mass ratio, and air flow rate) required to optimize reactor
yield. To achieve the maximum syngas production yield, experiments carried out using classical experimental
design methodology.
Keyword: biomass to fuel, downdraft gasifier, gasification, renewable energy, synthetic gas, thermochemical
conversion
I. INTRODUCTION AND BACKGROUND
Energy is the major facilitator of the modern
life. Every developed and developing economy
requires access to advanced sources of reliable
energy to support its growth and prosperity.
Nowadays, the present energy services have
enhanced the living in innumerable ways resulting an
inseparable relation between global population and
energy production. The relation between world
population and its demand on energy is shown Fig 1
[1].However, easily accebile energy supplies to
meetsociety demand has become challenging recently
due to societies enormous consumption. Fossil fuels
continues to be the primary source of energy with
coal, oil and natural gas contribution to around 87%
of global energy demands [2]. Fossil fuels are
generally considered non-renewable source of energy
as they cannot be easily re-generated in areasonable
time to be sustainable. The depletion of fossil fuels
compelssociety to explore alternative energy sources
to meet future world energy demands [3].
Figure 1-World population vs. energy demand
The transition from non-renewable energy
resources to renewable energy resources is
increasing, as the number of alternative renewable
energy choices expand to solar, wind, biomass and
geothermal energy. Recent studies show a 6%
increase in renewable energy use to supply society
energy during the past two decades from late 90’s to
2020 [4]. Apart from their depletion, fossil fuels
RESEARCH ARTICLE OPEN ACCESS

combustion release greenhouse gases (H2O, CO2) and
noxious emissions (NOX, CO) that have a severe
impact on the environment. In United States, about
90% of the greenhouse gases are due to combustion
of fossil fuels [5]. Biomass as a renewable energy
source, can serve to augment or replace for fossil fuel
to meet the increasing energy demand. In 2010,
renewable energy accounted for 16.7% of the world
energy supply with biomass contributing about 70%
(Fig 2) [6].
1.1 Biomass Gasification
Biomass is defined as organic matter derived
from dead or living organisms mainly composed of
carbon, hydrogen, oxygen, nitrogen and small
amount of sulfur and some heavy metals. As an
energy source, biomass can either be used directly via
combustion to produce heat, or indirectly after
conversion to various forms of biofuel. Three
common types of biomass are woody biomass, non-
woody biomass and animal or mankind. Among all of
these, wood is the largest sustainable source of
biomass energy [7]. Wood is a viable option for
replacement or augmentation of coal in industrial
combustors and gasifiers. To reduce carbon
emissions, variation of fuels is not the only option.
Other options include different conversion process
(i.e. digestion) and variation in conversion
technologies (i.e. gasifier). Among the technologies
available to produce energy from biomass,
gasification is relatively efficient method which is
generally environmentally benign. Gasification
represents a thermo-chemical conversion process that
convert carbonaceous material at elevated
temperatures to syngas. In general, the production of
heat and/or power with comparatively high efficiency
is possible using low BTU feedstocks such as
biomass, refinery residues or municipal wastes. This
process involves carbonaceous material at high
temperatures with a controlled amount of air
(oxygen) or steam. Biomass gasification process
typically consists of four main steps: drying,
pyrolysis, combustion and reduction. These steps
include both exothermic and endothermic chemical
reactions to produce the final syngas product. During
this process, steady operating involves the gasifier
maintaining a certain temperature profile [8]. Since it
produces no net increase in greenhouse gas (GHG)
emissions on a life-cycle basis (or absorbs the
amount of carbon dioxide emitted during the power-
production cycle), biomass gasification is considered
a carbon neutral process with environmental
advantages over conventional energy production [9].
The main product of biomass gasification is
commonly referred to as synthetic gas (syngas) which
is a mixture of CO, CO2, CH4 and H2.
Figure 2 -World energy consumption by source
1.2 Types of Gasifiers
Biomass gasifiers can be generally classified
into two broad categories: fixed bed and fluidized
bed. Various types of gasifier designs are briefly
explained below [10]. Fixed Bed Gasifier (updraft
and downdraft): the fixed bed is composed of
carbonaceous material and is classified by the flow of
gasifying agent (air/steam) through the gasifier [11].
Updraft Gasifier–simple, low cost design where
biomass enters from the top while air is entering from
the bottom. They are also known as counter flow
gasification, as shown in Fig 3 [12]. Hot syngas
produced in the gasifier passes up through the
pyrolysis and drying zones to heat raw feedstock.
Internal heat exchange between hot syngas and cooler
biomass feed produces low temperature syngas. The
main disadvantage of updraft gasifiers is that they
produce high amount of tar which needs to be
separated from syngas [13].
Downdraft Gasifier–Air moves concurrently with the
biomass feed entering from the upper part of the
gasifier. As shown in Fig 3, the grate supports the
fixed bed, where reduction occur followed by
combustion, pyrolysis and drying zone on the top
respectively. The tar produced in the pyrolysis zone
passes through the combustion zone where it is

cracked to produce more tar free syngas. This
represents the main advantage of this method. The
main disadvantage is using low density feedstock
which causes transportability or flow problems and
excessive pressure drop through the system and is
discussed in more detail later [14,15].
Figure 3 -Updraft and downdraft gasifiers
Fluidized Bed Gasifier (bubbling bed,
circulating fluidized bed): Feedstock particles are fed
from reactor side to a preheated granular (sand) bed,
where the air or steam is fed through the bottom to
fluidize biomass particles in the gasifier [11,16]as
shown in Fig 4 [17].The upward drag force of gas
thoroughly mixes the suspended solid particles inside
the gasifier with the air, thereby increasing the solid
fluid interactions compared to updraft or downdraft
gasifiers. The major advantage of fluidized bed
gasifiers is the uniform temperature profile in the
gasification zone created by circulating fluid through
fine granular material. Loss of fluidization due to
plugging the bed is the major disadvantages of
fluidized bed gasifier [15].
Figure 4 -Fluidized bed gasifier
1.3 Processing Zones in a Downdraft Gasifier
Drying Zone - is located at top entrance of the
gasifier. The main process occurring in this zone is
fundamentally dehydration or removal of moisture
content of the feed while no decomposition or
chemical reaction occurs. Biomass feedstock
normally has moisture content of 5 to 55%. The
dehydration process occurs at the temperature 150 -
250°F. The heat required for dehydration is
transferred mainly by conduction from the lower
zones in the gasifier.
Pyrolysis Zone-pyrolysis or devolatilization of the
feedstock involves thermal decomposition in the
absence of oxygen. The irreversible devolatilization
reactions take place in this zone at temperature
between 400o
F to 900o
F [18]. Energy required for
pyrolysis is supplied from combustion zone where
the exothermic reactions occur. Devolatilization
products include volatile, char and tar which accounts
for approximately 85% of feedstock. The volatile
component consists of mixture of H2, CO, CH4, H2O,
and CO2 along with heavy hydrocarbon which
condense into a black corrosive liquid tar. Char is the
solid carbon residue. The tar and char will further
undergo decomposition partial reduction in the
combustion and gasification zones. Pyrolysis and tar
cracking reactions occur to form primary tar
(expressed as C6.407H11.454O3.482) and secondary tar
(assumed as benzene) [19].
Volatile →0.268CO + 0.295CO2 + 0.094CH4 +
0.5H2 + 0.255H2O + 0.004NH3 + 0.2primary tar (1)
Primary tar →0.261secondary tar + 2.6CO +
0.441CO2 + 0.983CH4 + 2.161H2 + 0.408C2H4 (2)
Oxidation/Combustion Zone: supplies the energy for
the subsequent gasification and pyrolysis reactions.
All the oxidation reactions are exothermic in nature
and yield the temperature ranging from 1400°F to
2100°F. The carbon content of volatiles and chars
reacts with oxygen to form carbon dioxide whereas,
hydrogen and methane react with oxygen to produce
steam or water vapor and carbon monoxide [19].
C + O2 → CO2 (3)
H2 + ½ O2 → H2O (4)
CH4 + 1.5 O2 → CO + 2H2O (5)
Reduction/Gasification Zone: in this zone, a number
of high temperature chemical reactions between
different gaseous and solid reactants take place in the
absence of oxygen in a temperature range of 1100°F
and 1700°F. In general, the produced carbon dioxide,
water vapor, partially combusted volatiles, and chars
from above zones pass through the porous red hot
charcoal bed resting above the grate to undergo
reduction. The major reactions taking place in this
zone are water gas reaction and the Boudouard
reaction. The reduction reactions in this zone are
mentioned below [15,20]:
Water gas reaction
C + H2O → CO + H2
(6)
ΔH = +118.5 KJ/mol
Water shift reaction
CO + H2O → CO2 + H2
(7)
ΔH = -40.9 KJ/mol
Boudouard reaction
C + CO2 → 2CO
(8)
ΔH = +159.9 KJ/mol
Methanation reaction
C + 2H2 → CH4
(9)
ΔH = -87.5 KJ/mol

1.4 Applications of Gasification
Main applications of syngas are in Fischer
Tropsch process, bio-diesel production, electricity
generation, production of ammonia, methanol,
hydrogen and etc. [21]. The Fischer Tropsch is a
collection of chemical reactions that converts a
mixture of carbon monoxide and hydrogen into liquid
hydrocarbons, simply producing clean biofuels from
synthesis gas. Of all the major applications of
gasification, the electricity generation and Fischer
Tropsch process contributes to nearly about 50%.
According to the US department of energy, in 2009,
the potential of biomass usage in electricity
generation is projected to be 22 GW by the year 2022
[22].
II. DESIGN AND FABRICATION
The design and fabrication of the down draft
biomass gasifier to produce syngas, is the main
objective of this paper. The design is divided into
three sections namely, fixed bed reactor, transfer line
and the combustion chamber. The reactor, transfer
line and combustion chamber were fabricated from
carbon steel and black iron (see Fig 5).
2.1 Reactor
The down-draft fixed bed reactor consists of
two concentric cylinders called reactor core (inner)
and syngas plenum (outer) described below.
Reactor Core- The reactor core is the inner cylinder
made of carbon steel with an internal diameter of 8in
and a height of 19in. A wire mesh is attached via a
chain to the bottom of this cylinder to support the
biomass bed and also allow ash to exit the bed
continuously. A visual image of inside the reactor
core was possible via a HD camera connected to
process control computer, is place on the stand 4 ft
above the top opening of reactor shown in Fig
6.Syngas Plenum –A space between the inner and
outer cylinders is called syngas plenum which was
sealed with a donut shaped metal plate. The outer
cylinder was 20in diameter and 36in length. An
induced draft (ID) fan was installed between gasifier
and the combustion chamber to draw air into the
gasifier and transfer the produced syngas from the
reactor core to syngas outlet. Ash collected from the
biomass bed was removed through a valve at the
bottom of the syngas plenum. Gasifier effluent
flowing from the syngas plenum enters the transfer
line which included “tar-collection” devices. A
hopper mounted at the top of the reactor supplied a
continuous feed to the gasifier. The reactor also had a
small inlet to purge nitrogen during the shutdown
process to extinguish ongoing reactions. The thermal
profiles of the reactor were monitored using Lab
VIEW with three thermocouples placed inside each
zone in the reactor, Fig 7. These three thermocouples
were inserted at the height of 2”, 7.5” and 13” from
the reactor bottom which provided the temperatures
from each zones. The top thermocouple measured the
drying zone temperature around 150-250o
F followed
by combustion and gasification zones with average
temperature of around 1800o
F and 1500o
F
respectively measured by the middle and bottom
thermocouples.
2.2 Transfer Line/Tar Condensation System
A U-shape transfer line connected to the
syngas exit an ID fan was used to separate syngas
from tar. The transfer line had two valves at the
bottom of the “U” to collect the bio-oil (tar)
produced. An upstream ball valve was installed in
this section, to control the flow through the system,
set at 0 when fully closed and 8 when fully open. For
steady state operation valve was set between 2 and 3
to allow air into the gasifier. Velocity and flow rates
according to the setting are shown in Table 1. To
collect samples of produced gas, a T-junction
equipped with ball valve was placed after the ID fan.
This valve was normally closed which allowed all
syngas to be fed to the combustion chamber.
Figure 5 -Complete gasification process unit

Three thermocouples were attached in the
transfer line which were connected to the control
system, provided the temperatures of the product gas
coming from the gasifier (syngas out), going into the
fan (fan in), and exiting the fan to the combustion
chamber (fan out). Additionally, two oxygen sensors
were placed in the transfer line, one after the syngas
outlet and one before the combustion chamber. These
sensors measure the concentration of oxygen in
upstream and downstream gas to ensure no air leaks
into the system. To avoid flaming the gas mixture, it
is very important to maintain the oxygen
concentration in the flowing gas always below 1%
which results in a very rich mixture of syngas and
oxygen. The upper and lower flammable limit of
hydrogen (75% - 4%), carbon monoxide (75% -
12%), and methane (15% - 5%) confirmed that 1%
oxygen by volume in the mixture allowed the safe
operation. Oxygen sensors were always monitored
and recorded for safety operation. The components in
transfer line are shown in Fig5.
2.3 Enclosed Combustion Chamber
A carbon steel combustion chamber
(enclosed flare) was 24in diameterby44in high. A
final condensation section was connected to the feed
to the chamber via a 2in opening near the bottom of
the chamber.8 holes were included around the bottom
of the chamber allow air to be drawn into the chamber
to burn the syngas (Fig 8). A round gas (propane or
natural gas) burner was placed at the bottom center of
the chamber (Fig 9). Another HD camera was placed
outside of chamber to monitor and record the flame
through a window. Using glass fiber insulation, the
inner chamber surface was insulated to avoid a hot
external surface which would be a safety hazard and
lead to mechanical failure. A thermocouple was
placed at the top of the combustion chamber to
monitor the exhaust gas temperature prior to the
HVAC unit.
Figure 6 - Syngas flame and reactor core
Figure 7 - Temperature profiles, oxygen
concentrations
Figure 8 -Syngas feed line to combustion chamber
Table 1 -Velocity and flow of gas at different valve
setting
Setting Velocity1
(ft/min)
Flow2
(ft3
/min)
Setting 8 3170 69.15
Setting 7 3130 68.28
Setting 6 2130 46.46
Setting 5 1580 34.46
Setting 4 1150 25.08
Setting 3 680 14.83
Setting 2 320 6.98
Setting 1 25 0.545
Setting 0 0 0
1
Measured by hot wire anemometer
2
Determined by gas density, pipe diameter and
measured velocity

Figure 9 -Inside the combustion chamber with
support fuel
III. METHODOLOGY
The feed properties and the experimental procedure
used to run the gasifier are discussed below.
3.1 Biomass Feedstock Characteristics
Experiment were conducted considering
three different feeds includingpellets, flakes and chips
from oak and pine each with differentmoisture
content, heating value and bulk density.As shown in
Fig 10, the wood chipswereraw unprocessed high
moisturematerial obtained from Canadian paper mill,
and flakes and pellets werelow moisture processed
material. Flakes were processed wood without bark
and cut into small uniform sizes while pellets were
made from compactedoak saw dust.Five samples of
each type shown in Fig 8 were collected randomly
and proximate and ultimate analyses for each were
collected using a thermogravimetric analyzer and
CHN elemental analyzer, respectively. These
analyses were carried out on dry basis by placing
samples in a vacuum oven for nearly eight hours at a
temperature of 300o
F. The average proximate
analysis, ultimate analysis and heating value of these
feeds are shown in Table 2, Table 3and Table 4
respectively.
Table 2 - Proximate analysis
Component Chips Flakes Pellets
Moisture % 35.19 11.01 7.56
Volatile dry % 82.28 86.15 87.23
Fixed Carbon
dry %
17.26 13.32 12.39
Ash dry % 0.46 0.53 0.38
Table 3 - Ultimate analysis
Element % Chips Flakes Pellets
Carbon 48.81 48.24 49.03
Hydrogen 5.96 6.15 5.58
Oxygen 44.98 45.55 45.33
Nitrogen 0.26 0.06 0.06
Table 4 - Heating value
Heating value Chips Flakes Pellets
Cal/gr 4509.90 4562.12 4621.76
Btu/lb 8117.82 8211.82 8319.16
3.2 Experimental Method
The test procedure followed in these test
included these main steps: a) start up, b) steady state
continuous operation and c) shut down. Before
operating the system, a hazard and operability study
(HAZOP), is discussed below.
3.2.1 Hazard and Operability Study (HAZOP).
The HAZOP representeda structured and
systematic examination of a planned or existing
process and operating procedure to identify and
evaluate potential hazards that may represent risks to
personnel and/or equipment, or prevent efficient
operation [23]. The HAZOP conducted was a
qualitative measure, which aimed to stimulate the
imagination of participants to identify potential
hazards and operability problems. In this study, the
whole system was divided to separate nodes or sub-
systems including (1) the reactor core, (2) the syngas
plenum, (3) the tar trap, (4) the ID fan, (5) the solid
char removal, (6) the transfer line, (7) the sampling
branch and (8) the enclosed combustion chamber. For
each sub-system, the standard possible causes were
discussed which could lead to a dangerous situations.
The cause and consequence of each condition was
investigated and recommended remedies were
identified to control or avoid the hazardous condition.
A copy of final HAZOP spreadsheet was prepared
and signed by all operators and people represented
from environmental health and safety who
participated in HAZOP.
Figure 10 -Left to right: pellets, flakes and chips

3.2.2 Start Up. Following the HAZOP, the following
procedure was used to safely operate the gasifier.
Combustion chamber was preheated by igniting the
propane burner in the enclosed flare and starting the
ID fan. Ten lb. of biomass was loaded into the reactor
core and was ignited from the top. While the biomass
was burning the upstream valve controlling air flow
through the ID fan was set to 3 to pull the produced
gas and smoke through the reactor and into the
enclosed flare. As the reactions proceeded, the
temperature increased to 1600-1800℉ in combustion
zone. Simultaneously both oxygen sensors showed
approximately 0.6-0.8 O2%. Remaining ash was
removed from the bed through the ash grate. To
enhance the flow, a vibrator attached to the inner
cylinder was turned on to minimize bridging inside
the reactor.
3.2.3 Steady State Operating Procedure.
Approximately 4-8 lb of biomass feed (depending on
feed type) was fed once the combustion zone was
established. The temperature profiles of zones
decreased following addition of the feed since it was
at room temperature and had moisture. The
temperatures increased again to steady state levels in
combustion and gasification zones. During the steady
state operation, the gasification zone (bottom of
reactor) had a temperature of 1400o
F while the
combustion zone (located above the gasifier zone)
had a temperature of 1600-1800o
F. By opening the air
flow control valve, more air was fed into the reactor
which resulted in increase in combustion and
gasification zones temperatures. As the biomass were
gasified through the reactor, new feed was added to
the reactor and the above procedure was repeated for
the steady state operation. Processing rates of biomass
were between 0.5 to 1.5 lb per minute depending on
the type of the feed. To acquire the produced gas
composition, samples were taken through the
sampling branch located after the ID fan, before
entering the combustion chamber. Taken samples
were analyzed by a Gas Chromatography (GC) unit.
3.2.4 Shutdown. The ID fan was turned off and
nitrogen was purged until the gasification reactions
were extinguished. Then, the air flow control valve
was closed and the top of the reactor was sealed,
isolated the whole gasifier from the transfer line and
combustion chamber which prevented air/gas from
entering to or coming out from the reactor.
Temperatures of the combustion and gasification
zones decreased rapidly and then cooled down slowly
for a full shutdown. It takes approximately 2 minutes
to shut down the system and 3-5 hours for complete
cool-down to room temperature. Finally, char
remaining in the reactor was vacuumed out and tar
collected was removed from the transfer line.
IV. RESULTS AND DISCUSSION
Experiments were conducted for oak pellets,
pine flakes and chips in the down draft biomass
gasifier. The following section presents the results
from these tests. The optimum operating conditions
for the three feeds used in this experiments were
found to be different given their composition and
transportability.
4.1 Pellets
Fuel pellets made from compacted sawdust
with a very low moisture content and high heating
value were most transportable which avoided any
bridging in the bed (compared to wood chips and
flakes). Given the low moisture content, the pellets
also ignited most easily and produced the highest
syngas quality.
In addition to the air flow control valve, it
was observed that the air flow into the reactor was
affected by the amount of raw feed on the top of
combustion bed. Depending on the feed type, the
feeding rate should be optimized to get the proper air
flow into the reactor. Too much air increases the
temperature in combustion and gasification zones and
results in pure combustion of the feedstock. On the
other hand, lack of enough air stops the combustion
reactions and consequently the gasification process.
Temperature profiles inside the reactor core are
shown in Fig 11.
As shown in Fig 11, the experiment was
started at 11:51AM by igniting the pellets. The
temperature in combustion and gasification zones
were the key indicators to add a new pile of feed.
Usually 1500o
F for combustion and 1200o
F for
gasification are the good temperatures to start feeding
the reactor. At 12:10PM, when the desired
temperatures were achieved, a new pile of pellets was
added to the reactor. The shutdown process was
started at 2:43PM by turning the ID fan off, sealing
the top opening of the reactor and purging nitrogen
through the bed. Air flow control valve was kept open
for less than a minute to let the nitrogen extinguish
the reactions and sweep the whole system, and then
closed to isolate the reactor.

Figure 11 - Pellets temperature profiles inside the reactor core
Figure 12 - Temperature profiles in the transportation unit for pellets
The temperature of syngas leaving the
gasifier was directly related to the temperatures of
gasification and combustion zones which were a
function of air flow into the reactor. The produced
syngas was cooled down (usually from 500o
F to
200o
F) through the transfer line and bio-oil was
collected through two outlets in the transfer line
before the ID fan. The temperature of syngas coming
out of the gasifier was always controlled (<500o
F) to
avoid damaging the ID fan. Temperatures profiles of
syngas outlet, fan inlet and fan outlet are shown in
Fig 12.
4.2 Flakes
Like pellets, flakes (wood shavings) are also the
processed materials with slightly higher moisture
content. Flakes flowed much harder through the
reactor compared to pellets. To assist the flow of
flakes through the bed, a vibrator was attached to the
inner cylinder of the reactor. Since flakes had much
lower density than the other two feed stocks in this
study, they were processed in a lower mass rate. This
is not to be confused with the volumetric rate of
processing of flakes which was much higher than
pellets and picks, given its shape and void fraction in
bulk. The temperature profiles inside the reactor and
through the transportation are shown in Fig 13 and
Fig14.
Figure 13 - Flakes temperature profiles inside the reactor core

Figure 14 - Temperatures profiles in transportation unit for flakes
4.3 Chips
It was very difficult to start up the
experiment using only chips, since they had 35%
moisture. So, there were two solutions for this
problem: 1. pre-dry the chips or 2. mix them with
pellets just for startup. In this experiment, option 2
was chosen since it was more economic and simple.
Once a good combustion zone was achieved, then
chips were added for steady state operation. Less than
flakes and more than pellets, chips had a hard time to
flow through the reactor. So, bridging and void
creation were expected in the absence of vibrator.
Since chips had the highest moisture content
comparing to the other two feeds, it was
recommended to run the gasifier at very low feed rate
to avoid dramatic temperature drop in combustion
and gasification zone sand maintain a stable
combustion bed and steady state operation. The huge
temperature drop at times 3:34 PM and 3:40 PM in
Fig15occurred when large piles of chips were added
to the system.
From the camera looking into combustion
chamber, it was observed that the syngas flame from
chips was less dense and stable compared to pellets.
This indicated the low heating value of the produced
syngas from wood chips with high moisture contents.
Temperature profiles inside the reactor core and
through the transfer line are shown in Fig 15and Fig
16.
4.4 Syngas Composition and Bio-Oil/Tar
Production
The composition of syngas produced from
pellets gasification process is shown in Table 5.
These values will vary if pure oxygen was used
instead of air as gasification medium. From the
result, H2 and CO as main components of interest
shared about 40% of the total volume of the produced
gas. On the other hand, a dark color liquid fuel, bio-
oil/tar was formed as a side product of pyrolysis
reaction. During the pyrolysis reaction,
carbonaceous biomass feedstock underwent thermal
degradation to form volatiles, char and ash. In case of
low temperature and cold startup, these volatiles
condensed and formed a brownish black thick liquid
known as wood oil or bio-oil. Mainly it consists of
70% carbon, 7-9 % hydrogen and 20% oxygen. It has
significant amount of 20-30% miscible water
depending on the moisture contents of biomass
feedstock. The quality and composition of this bio-oil
also rely on the type of pyrolysis and the composition
of feedstock. Like biomass, bio-oil is also more
environmental friendly fuel with less CO2 and SO2
emissions comparing to fossil fuels. It has a heating
value of 25-30 MJ/Kg which is 25-35% lower
compared to crude oil [18,24].A picture of bio-oil
that was collected during the startup process is shown
in Fig 17.
Figure 15 - Chips temperature profiles inside the reactor core

Figure 16 - temperature profiles in transportation unit for chips
Table 5 - Syngas composition
Component Volume %
Hydrogen 18
Carbon monoxide 21
Carbon dioxide 16
Methane 2
C2
+
Hydrocarbons 2
Nitrogen 41
Figure 17 -Collected bio-oil during startup
V. CONCLUSION AND ONGOING WORK
A one ton per day downdraft biomass
gasifier was designed, fabricated and operated to
produce syngas, and various biomass feedstock
including pellets, flakes and high moisture chips were
successfully processed in the designed unit. All
experiments were recorded and temperature profiles
inside the reactor and through the transfer line were
presented as well as syngas composition and bio-oil
properties. Sensitivity analysis was performed to find
out the effects of bed temperature, air flow rate and
feed moisture content on the syngas production.
Biomass feed rate and air flow rate into the
reactor played important roles to maintain steady
state operation. So, an optimum level of feed rate
and air flow rate were required to retain the steady
state conditions. To maintain the process, higher air
flow rate was required whenever feed rate was
increased. It was also discussed that the feeds were
different in terms of rate of combustion and
gasification. Having higher density, higher heating
value, lower moisture and cylindrical shape, pellets
were transported easier through the reactor,
maintained more stable combustion zone, and
produced more stable and dense syngas flame
comparing to chips and flakes. To study the effect of
reactor size on the rate of production of syngas which
is expected not to be linear, a scaling project is
planned which includes changing the reactor core
diameter down to 4in and up to 12in instead of the
existing 8in. Also, the change in temperature profiles
through the reactor and possibility of having a stable
and uniform combustion zone in a very large
diameter reactor will be studied. The change in the
amount of heat loss will be studied too since the
surface area to volume ratio will change when the
reactor diameter is changed while keeping the same
height.
REFERENCES
[1] National Energy Technology Laboratory,
Energy Predicament,(2011)
[2] U.S. EIA International Energy
Statistics,(2010);http://www.eia.gov/cfapps/i
pdbproject/IEDIndex3.cfm
[3] McKendry, P., Energy production from
biomass (part 1): Overview of biomass.
Bioresource Technology, (2002) 83(1): p.
37-46
[4] World Energy Resources,(2013) Survey:
Summaryhttps://www.worldenergy.org/wpc
ontent/uploads/2013/10/WEC_Resources_su
mmary-final_180314_TT.pdf
[5] Inventory of U.S. Greenhouse Gas
Emissions and Sinks: 1990 – 2013 APRIL
15, (2015) U.S. Environmental Protection
Agency

https://www3.epa.gov/climatechange/Downl
oads/ghgemissions/US-GHG-Inventory-
2015-Main-Text.pdf
[6] Renewables 2012 Global status report.
World Energy Consumption, 2012);
https://en.wikipedia.org/wiki/Renewable_en
ergy#/media/File:Total_World_Energy_Con
sumption_by_Source_2010.png.
[7] Gai, C. and Y. Dong, Experimental study on
non-woody biomass gasification in a
downdraft gasifier. International Journal of
Hydrogen Energy, (2012) 37(6): p. 4935-
4944.
[8] Kumar, A., D.D. Jones, and M.A. Hanna,
Thermochemical Biomass Gasification: A
Review of the Current Status of the
Technology. Energies, (2009) 2(3): p. 556-
581.
[9] Bracmort, K., Is Biopower carbon neutral?
Congressional Research Service, (2015)
[10] Rajvanshi, A.K., BIOMASS
GASIFICATION. Alternative Energy in
Agriculture,(1986) Vol. II: p. 83-102.
[11] FAO, FORESTRY, PAPER 72, Wood gas
as Engine fuel, Rome, Italy,(1986)
http://www.fao.org/3/a-t0512e.pdf
[12] ASHDEN sustainable solution, better
lives,(2016)https://www.ashden.org/biomass
-gasification
[13] Dhruv S Deshpande, A.D.P., Shailesh L
Patil, Anirudha G Ghadge, V. N. Raibhole*,
Testing And Parametric Analysis Of An
Updraft Biomass Gasifier. International
Journal of ChemTech Research, (2013).
Vol.5 (No.2 ): p. 753-760
[14] Sastry, A.B.a.R.C., Biomass Gasification
Processes in Downdraft Fixed Bed Reactors:
A Review. International Journal of Chemical
Engineering and Applications, December
(2011). Vol. 2(6).
[15] Patra, T.K. and P.N. Sheth, Biomass
gasification models for downdraft gasifier:
A state-of-the-art review. Renewable and
Sustainable Energy Reviews, (2015). 50: p.
583-593
[16] Muilenburg, M.A., COMPUTATIONAL
MODELING OF THE COMBUSTION
AND GASIFICATION ZONES IN A
DOWNDRAFT GASIFIER, in Mechanical
Engineering,(2011). The University of Iowa,
Iowa City, Iowa
[17] Bubbling fluidized bed gasification,
ANDRITZ international technology group
https://www.andritz.com/products-and-
services/pf-detail.htm?productid=14969
[18] YounesChhiti, M.K., Thermal Conversion of
Biomass, Pyrolysis and Gasification: A
Review. The International Journal of
Engineering and Science (IJES), (2013).
Volume 2(Issue 3): p. 75-85
[19] Yueshi Wu, Q.Z., Weihong Yang and
WlodzimierzBlasiak, Two-Dimensional
Computational Fluid Dynamics Simulation
of Biomass Gasification in a Downdraft
Fixed-Bed Gasifier with Highly Preheated
Air and Steam. Energy Fuels, (2013)Vol. 27,
no 6, 3274-3282 p.
[20] Dejtrakulwong, C. and S. Patumsawad, Four
Zones Modeling of the Downdraft Biomass
Gasification Process: Effects of Moisture
Content and Air to Fuel Ratio. Energy
Procedia, (2014). 52: p. 142-149.
[21] Rauch, H.B.a.R., Review Applications of
Gases from Biomass Gasification (2006).
“Syngas production and utilization” in the
Handbook Biomass Gasification. Biomass
Technology Group.
[22] Bain, R.L.,USA Biomass Gasification
status. IEA Bioenergy Task 33,National
Renewable Energy Laboratory,
NREL(2012)
[23] British Standard BS: IEC61882:2002
Hazard and operability studies (HAZOP
studies) - Application Guide British
Standards Institution
[24] Dinesh Mohan, C.U.P., Jr., and Philip H.
Steele, Pyrolysis of Wood/Biomass for Bio-
oil: A Critical Review. Energy and Fuels,
(2006). 20: p. 848-889

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